COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 107 CIVIL AVIATION SAFETY AUTHORITY
SCHEDULE OF AIRWORTHINESS DIRECTIVES
Radio Communication and Navigation Equipment
AD/RAD/66 Mode S Altitude 12/99 DM
Applicability: All aeroplanes equipped with one or more Mode S transponder systems connected to a TCAS II.
Requirement: 1. Determine the source(s) of pressure altitude data to the Mode S transponder(s) by inspection and reference to the build standard of the aircraft, together with the Maintenance Manual and Wiring Diagram Manual.
2. Following the determination at Requirement 1, action as follows:
- For aircraft using altitude data input to the Mode S transponder(s) and encoded in other than Gilham format (eg databus or synchro formats), no further action is necessary.
b. For aircraft where altitude data is encoded in Gilham format and inputs to each Mode S transponder are provided from dual altitude encoders:
(i) For each transponder confirm, by inspection and reference to both aircraft and equipment Maintenance Manuals and Wiring Diagram Manuals, that the transponder altitude comparator function is enabled, and, using appropriate test equipment, demonstrate that the comparator detects altitude data differences between the dual encoders of more than 600 feet.
(ii) Amend the approved System of Maintenance to provide a verification test of the functionality of the transponder altitude data comparator at periods not to exceed 24 calendar months.
c. For aircraft where altitude data in Gilham format is provided to each Mode S transponder from a single altitude source:
(i) Test the systems using appropriate test equipment to verify that the altitude readout of the Mode S is correct throughout the operating envelope of the aircraft.
3. If, as a result of the Requirement 2.b.(i) inspection/test, the altitude comparator function is found not to be enabled or is unserviceable, enable and/or rectify the comparator.
Note 1: CAA(UK) AD 001-08-99 refers.
Compliance: 1. Within 45 days from the effective date of this Directive.
2. b. (i) Within 45 days from the effective date of this Directive.
COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 107 CIVIL AVIATION SAFETY AUTHORITY
SCHEDULE OF AIRWORTHINESS DIRECTIVES
2. b. (ii) Within 90 days from the effective date of this Directive.
2. c. (i) Within 45 days from the effective date of this Directive and thereafter at intervals not to exceed 45 days until the aircraft is modified with either a single monitored air data sensor or dual independent altitude encoders and an altitude data comparator.
Note 2: The modification of the aircraft is an optional terminating action only, modification is not required by this Directive.
3. Before further flight.
This Airworthiness Directive becomes effective on 13 October 1999.
Background: The CAA(UK) and the Bureau of Air Safety Investigation have reported incidents where a potentially hazardous loss of separation occurred. One incident resulted from faults in the Mode S system in one of the aircraft were erroneous altitude data was being transferred to the TCAS II equipment. This transfer of the erroneous data resulted from a dormant fault in an altitude data source comparator, installed in the Mode S transponder.
This Directive requires confirmation that the altitude comparator is enabled or, where there is only single altitude data source, the repetitive checking of the Mode S altitude readout.
Overview
The Civil Aviation Regulations 1998, specifically Part 39 - 107 under the Civil Aviation Safety Authority, includes a schedule of Airworthiness Directives aimed at enhancing aviation safety. AD/RAD/66, enacted in 1999, addresses the problem of erroneous altitude data being transmitted from Mode S transponders to Traffic Collision Avoidance System (TCAS II) equipment, which had been identified as a cause of potentially hazardous loss of separation between aircraft. The policy objective of this directive is to ensure that all aeroplanes equipped with Mode S transponders have accurate and reliable altitude data, thus preventing incidents related to incorrect altitude information. This was enacted by the Commonwealth of Australia to meet safety standards set by the Civil Aviation Safety Authority and aims to mitigate risks associated with faulty altitude data sources in Mode S systems.
Scope and Application
The Civil Aviation Safety Authority (CASA) has issued Airworthiness Directive AD/RAD/66, which applies to all aeroplanes equipped with one or more Mode S transponder systems connected to a TCAS II, ensuring the safety of radio communication and navigation equipment. This regulation mandates that operators determine the source(s) of pressure altitude data to the Mode S transponder(s) and take appropriate action based on the format and redundancy of the altitude data. Specifically, for aircraft where altitude data is encoded in Gilham format and inputs to each Mode S transponder are provided from dual altitude encoders, it is essential to confirm that the transponder altitude comparator function is enabled and can detect altitude data differences exceeding 600 feet. Additionally, operators must modify their maintenance system to include a verification test of the transponder altitude data comparator at intervals not exceeding 24 calendar months. For aircraft with a single altitude source in Gilham format, operators must verify the correctness of the altitude readout throughout the aircraft's operating envelope using appropriate test equipment. Any identified issues with the altitude comparator function must be rectified before further flight. Compliance with this directive must be achieved within specified timeframes from its effective date of 13 October 1999.
Key Provisions
The Civil Aviation Regulations 1998, specifically Part 39 - 107 under the Civil Aviation Safety Authority Schedule of Airworthiness Directives, AD/RAD/66, pertains to Mode S Altitude requirements for aeroplanes equipped with Mode S transponder systems connected to a TCAS II. Section 1 of the directive requires operators to determine the source of pressure altitude data to the Mode S transponder by inspecting and referring to the aircraft's build standard, Maintenance Manual, and Wiring Diagram Manual (subsection 1). Based on the type of altitude data input, operators must take specific actions. For aircraft using altitude data input in other than Gilham format, no further action is necessary (subsection 2(a)). However, for aircraft where altitude data is in Gilham format and inputs are provided from dual altitude encoders, operators must ensure the transponder altitude comparator function is enabled and capable of detecting altitude data differences of more than 600 feet between the dual encoders, using appropriate test equipment (subsection 2(b)(i)). Moreover, operators must amend the approved System of Maintenance to include a verification test of the transponder altitude data comparator at intervals not exceeding 24 calendar months (subsection 2(b)(ii)). For aircraft where altitude data is in Gilham format but provided from a single altitude source, operators must test the system to verify the accuracy of the Mode S altitude readout throughout the aircraft's operating envelope (subsection 2(c)(i)). If the altitude comparator function is found to be unserviceable during the inspection and testing, operators must rectify or enable the comparator before further flight (subsection 3).
Operators must comply with the directive within specified timeframes. For the actions in subsections 1, 2(b)(i), and 2(c)(i), compliance must be achieved within 45 days from the effective date of the directive (subsection 1, 2(b)(i), and 2(c)(i)). For the amendment of the System of Maintenance as outlined in subsection 2(b)(ii), compliance must occur within 90 days from the effective date of the directive. This compliance must continue at intervals not exceeding 45 days until the aircraft is modified with either a single monitored air data sensor or dual independent altitude encoders and an altitude data comparator (subsection 2(b)(ii)). Modification of the aircraft is optional and not mandated by the directive, but compliance with the testing and verification requirements is mandatory.
Failure to comply with the requirements of the Airworthiness Directive may result in legal consequences. The specific penalties are not detailed within the text of the directive itself, but under general civil aviation regulations, non-compliance could potentially lead to enforcement actions by the Civil Aviation Safety Authority (CASA), which may include fines, suspension or revocation of air operator certificates, or other regulatory penalties. These consequences underscore the importance of adhering to the directive to ensure the safe operation of aircraft and the prevention of hazardous incidents.